- A
Continue using the NAT Gateway but reduce CloudWatch log retention to 1 day.
Why wrong: Reducing log retention can lower CloudWatch storage costs, but it does not reduce NAT Gateway data processing charges for outbound API calls from the workload.
- B
Replace the NAT Gateway route with VPC endpoints: use a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager.
VPC endpoints provide private connectivity to AWS services without sending traffic through the internet or through NAT. A Gateway endpoint is used for S3, and an Interface endpoint is used for services like Secrets Manager. Traffic to those services stays within the AWS network, reducing or eliminating NAT charges for those API calls.
- C
Launch a bastion host in a public subnet and force private instances to use SSH tunneling for API calls.
Why wrong: SSH tunneling adds complexity and does not inherently remove NAT data charges. The bastion would still require outbound connectivity paths, which typically still involve NAT if access is not otherwise endpoint-based.
- D
Switch to public subnets and attach security groups with the same rules to limit inbound access.
Why wrong: Moving to public subnets changes the exposure model and does not satisfy the requirement to avoid traversing the public internet. It also may not reduce NAT-related billing in the intended way.
Quick Answer
The answer is to replace the NAT Gateway route with VPC endpoints: a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager. This directly reduces NAT Gateway cost because VPC endpoints allow private subnets to reach AWS services without traversing the public internet or incurring NAT data processing charges; Gateway endpoints use route table entries to pull S3 traffic directly, while Interface endpoints attach a private elastic network interface for services like Secrets Manager, keeping all traffic within the AWS network. On the SAA-C03 exam, this scenario tests your understanding of cost optimization through private connectivity—a common trap is assuming a NAT Gateway is required for all outbound traffic, when in fact VPC endpoints eliminate the need for it entirely. Remember the memory tip: “Gateway for S3, Interface for the rest” to quickly recall which endpoint type pairs with which service.
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service runs in private subnets. It must call AWS APIs (for example, S3 and Secrets Manager). The team currently sends all outbound traffic through a NAT Gateway, and NAT charges have become a major cost driver. The workload must not traverse the public internet. What change most directly reduces NAT Gateway cost while maintaining private connectivity to those AWS services?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Replace the NAT Gateway route with VPC endpoints: use a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager.
Option B is correct because VPC endpoints allow private connectivity to AWS services without traversing the internet or a NAT Gateway. A Gateway VPC endpoint for S3 uses route table entries to reach S3 privately, and an Interface VPC endpoint for Secrets Manager uses an elastic network interface with a private IP. This eliminates NAT Gateway data processing charges entirely while keeping traffic within the AWS network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Continue using the NAT Gateway but reduce CloudWatch log retention to 1 day.
- ✓
Replace the NAT Gateway route with VPC endpoints: use a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager.
Why this is correct
VPC endpoints provide private connectivity to AWS services without sending traffic through the internet or through NAT. A Gateway endpoint is used for S3, and an Interface endpoint is used for services like Secrets Manager. Traffic to those services stays within the AWS network, reducing or eliminating NAT charges for those API calls.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Launch a bastion host in a public subnet and force private instances to use SSH tunneling for API calls.
- ✗
Switch to public subnets and attach security groups with the same rules to limit inbound access.
Why it's wrong here
Moving to public subnets changes the exposure model and does not satisfy the requirement to avoid traversing the public internet. It also may not reduce NAT-related billing in the intended way.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think NAT Gateway is the only way to provide outbound connectivity, overlooking that VPC endpoints can provide private, cost-effective access to AWS services without internet routing.
Detailed technical explanation
How to think about this question
Gateway VPC endpoints (for S3 and DynamoDB) work by adding prefix lists to the route table, enabling direct traffic over the AWS backbone without leaving the VPC. Interface VPC endpoints (for Secrets Manager, STS, etc.) use AWS PrivateLink, which creates an ENI in the subnet and routes traffic through it, incurring hourly charges but no data processing fees per GB like NAT Gateway. In high-traffic scenarios, this shift can reduce costs by 70–90%.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Replace the NAT Gateway route with VPC endpoints: use a Gateway VPC endpoint for S3 and an Interface VPC endpoint for Secrets Manager. — Option B is correct because VPC endpoints allow private connectivity to AWS services without traversing the internet or a NAT Gateway. A Gateway VPC endpoint for S3 uses route table entries to reach S3 privately, and an Interface VPC endpoint for Secrets Manager uses an elastic network interface with a private IP. This eliminates NAT Gateway data processing charges entirely while keeping traffic within the AWS network.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Same concept, more angles
1 more ways this is tested on SAA-C03
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Based on the exhibit, your application runs entirely in private subnets and only needs to reach Amazon S3, Amazon DynamoDB, AWS Secrets Manager, and CloudWatch Logs. The monthly bill is dominated by NAT Gateway charges. Which change most directly reduces cost while preserving private connectivity to these AWS services?
hard- A.Replace the NAT Gateway with an Internet Gateway and keep the current private subnet routes unchanged.
- B.Add a second NAT Gateway in another Availability Zone to reduce cross-AZ data transfer charges.
- C.Create only interface endpoints for all four services and keep the NAT Gateway for fallback.
- ✓ D.Create S3 and DynamoDB gateway endpoints, create interface endpoints for Secrets Manager and CloudWatch Logs, update route tables, and remove the NAT Gateway.
Why D: Option D is correct because it replaces the costly NAT Gateway with free VPC Gateway Endpoints for S3 and DynamoDB, and uses AWS PrivateLink interface endpoints for Secrets Manager and CloudWatch Logs. This eliminates all internet-bound data transfer costs while keeping traffic entirely within the AWS network, directly addressing the cost concern without sacrificing private connectivity.
Last reviewed: Jun 11, 2026
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.
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